Grazing Strategies to Control Medusahead in California

2007 Annual Report for SW06-038

Project Type: Research and Education
Funds awarded in 2006: $138,539.00
Projected End Date: 12/31/2010
Region: Western
State: California
Principal Investigator:

Grazing Strategies to Control Medusahead in California


We studied precision grazing to control medusahead. High-density short-duration grazing when medusahead is at the internode elongation and boot stages dramatically reduces medusahead infestation. Susceptible phenological stages are predictable but vary over regions. Low-moisture supplement placed in medusahead patches increases grazing intensity, but the effect is localized. Wider supplement distributions will be tested. Results and approaches were disseminated in several regional and national meetings, and by direct communication with producers. Discussions with stakeholders resulted in recommendations to test mowing and non-selective herbicides as additional control tools that can be used with a precision approach. Progress was better than satisfactory.

Objectives/Performance Targets

1. Design a simple and cost-effective “precision” grazing method to control medusahead, and incorporate it into the grazing systems of California annual rangelands.

2. Study the effects of spatial distribution of attractants such as supplement on spatial distribution of grazing pressure, and use new knowledge to implement supplementation methods to reduce medusahead infestations.

3. Develop and implement a site-specific and simple system to identify and forecast the period of greatest susceptibility of medusahead to mowing and grazing, and establish a warning system for ranchers to accurately time grazing.

4. Disseminate, demonstrate, and document results in extension fact sheets, field visits, and newsletters by Farm Advisors.


Experiments and measurements

We conducted four series of activities at private ranches:
1. One grazing/reseeding and two mowing experiments.
2. Use of low moisture blocks as attractants for cattle in six ranches.
3. Detailed classification and records of medusahead phenology in eleven counties of California.
4. Two germination and seeding experiments.

Precision grazing with sheep to control medusahead

We conducted a fully replicated grazing experiment where sheep were used at high density for a short duration during the period of peak medusahead susceptibility to grazing (internode elongation to boot stage). Sheep weighed about 90 kg. We used combinations of high and low animal density with short and long grazing periods to obtain a series of levels of utilization. After grazing, half of each plot was broadcast-seeded with a mixture of Bromus hordeaceus, Elymus elymoides (squirreltail), Lolium multiflorum, Trifolium hirtum, and Trifolium suberraneum (subclover) and Bromus carinatus (California brome) during the fall of 2007 following the first fall rains. Soil was prepared by a very light disking to a depth of 1-2 cm and seed was covered with a light chain harrow.
Herbage botanical composition, mass, and nutritional quality were measured before grazing and after animals were removed from each plots. Additional measurements were completed the end of the growing season in 2007 to determine seed production by medusahead, and will be repeated at the peak of the following season (2008) to determine degree of control. Botanical composition by species was assessed visually. Herbage growth and disappearance were assessed by establishing two areas where grazing was excluded in each plot, and by measuring herbage mass before and after grazing outside the exclosures, and after grazing inside the exclosures.

Stocking rates applied varied between 1.06 to 2.12 AUM ac-1. Each sheep was estimated to be 0.25 AU. Herbage disappearance rate (kg DM sheep-1 day-1) was not affected by sheep density or total grazing duration, averaging 11.7 ± 0.81 kg DM sheep-1 day-1. Herbage growth was not considered because of the short grazing period and extremely dry conditions. There was a tendency of longer grazing periods to have greater mass disappearance for any given stocking rate. Daily intake per sheep estimated on the basis of 3 % body mass should be about 2.85 kg day-1, which is only 24 % of the change in herbage mass. This is interpreted a the trampling effects on the standing dead mass that was composed mostly of medusahead from the previous two grazing seasons.

Herbage mass included all aboveground mass, including standing dead and litter. Medusahead litter and standing dead mass was abundant in many plots. Samples will be hand-sorted into live medusahead, litter and standing dead, and other species. The present results are based on all herbage, standing dead and litter mass. Future analyses will express results on the basis of green herbage mass and dead medusahead mass as a potential grazing deterrent.

The relationship between herbage disappearance and stocking rate yielded a rate of mass disappearance per sheep day equal to 13.9 ± 2.93, which is not significantly different from the estimate obtained above by directly averaging the values for each plot.

Level of utilization in each plot was assessed visually every other day to determine if a predetermined nominal utilization had been achieved. Once the nominal utilization was estimated to be reached, animals were removed from the plot under consideration. Although there was a good relationship between estimated and actual utilization, utilization was controlled better simply by setting the stocking rate.

Although the final impact of grazing treatments on medusahead has to be based on the population of medusahead during the spring of 2008, seed production at the end of the grazing season is an indicator of the impact on weed reproduction. A preliminary estimate indicated that medusahead seed production was 820 ± 310 and 14640 seeds m-2 in grazed and ungrazed areas. Grazing was effective in reducing medusahead seed production.

Mowing experiments

Effect of timing and intensity of defoliation on medusahead and goatgrass reproduction

Two 6 m x 26 m areas were used in this study, one dominated by goatgrass and the other dominated by medusahead. In each area we established 54 50 cm x 50 cm plots separated by 50 cm alleys. A factorial of dates and heights of defoliation treatments were replicated twice in a completely randomized design. Defoliation intensities (heights) were 3, 6, and 9 cm from the ground. The nine defoliation dates were April 15, 19, 25, 28, and May 1, 4, 8, 12, 16, 2007. Canopy height and botanical composition of the defoliated plots were surveyed before defoliation and at the end of the season. Each plot was defoliated once and then left undisturbed until the end of the season. Immediately prior to defoliation, five plants of medusahead or barbed goatgrass were collected from each plot to determine their phenological stage according to Table 1. Clipped herbage from each plot was collected and dried to determine biomass and number of seedheads. A final survey of botanical composition, number of seedheads of medusahead and barbed goatgrass, and canopy height of all defoliated plots was conducted on July 12, 2007. Data were analyzed by ANOVA. Medusahead and goatgrass were analyzed as separate experiments, because they were in separate areas.

Table 1. Phenological stages of medusahead that are relevant for its management and control.
Stage Code Description
V1 Plant Germinated
V2 Early vegetative, before elongation of internodes
V3 Late vegetative, elongation of internodes and boot stage
R4 From emergence of awns to full emergence of seedhead
R5 From fully emerged seedhead to opening of florets. Anthesis. Visible anthers.
R6 Anthesis to closure of florets. Beginning of kernel formation.
R7 Kernel elongation inside floret until it reaches full length.
R8 Seeds in milk stage. Kernels occupy full length of palea.
R9 Seeds in dough stage.
M10 All seeds in seedhead are mature and hard. Plants are not dead yet. There is some red, brown and green in the seedheads. Glume veins are dark.
D11 Tiller is dead and dry. Color is uniform, sandy yellowish but not grey. Seeds shatter.
L12 Grey plant remains obviously from the previous season.

Defoliation of medusahead as early as 15 Apr had a major impact on seedhead production, whereas barbed goatgrass exhibited significant seed production for mowing dates earlier than 28 April. Overall, goatgrass exhibited better ability to recover from defoliation than medusahead, which makes it harder to control with mechanical means.
The results of our research showed that mechanical defoliation is an effective method for the control of medusahead and barbed goatgrass. The best time for defoliation is at the phenological stage R5 (visible anthers) because there is not chance that plants will grow new tillers and there are not seeds even beginning to form. This confirmed the point that the optimum time for mowing most annual weeds is in the flowering stage before seed development. The late phenology of medusahead allows desirable forage species such as Bromus hordeaceus, Lolium multiflorum, Trifolium hirtum and Erodium botrys growing with medusahead and barbed goatgrass to set seed prior to mowing, thus maximizing the positive impact on the grassland.
Defoliation at stage R5 can reduce medusahead and barbed goatgrass seed production by almost 100%. Based on these results, the recommended height for defoliation is from 3 cm to 6 cm. Final evaluation of impact of mechanical defoliation will be based on the botanical composition in the spring of 2008.

Medusahead has invaded a large proportion of the Dunnigan Hills region of Yolo County, California. This region is characterized by gentle slopes and little presence of rocks. Most areas have a history of rain fed barley production. Old fields have very high density of medusahead, which reduces the grazing value. This area is characterized by very heavy medusahead infestation, to the point that in some patches medusahead thatch has accumulated to the point that it smothers itself. One rancher contacted our group for advice about mowing and we established a trial to determine the effectiveness of mowing with commercial machinery.

We established five transects in the area to be mowed and determined botanical composition by visual estimation of cover. Medusahead cover ranged from 47 ± 5.4 to 23 ± 4.6 %. The other main species were Torilis sp., Trifolium hirtum, Vicia sp., Bromus hordeaceus and Avena barbata. Several swaths were mowed across the transects on 7 May 2007. Preliminary measurements taken on 4 June 2007 indicated that medusahead seed production in mowed and control areas were 140 ± 35 and 3030 ± 900 seeds m-2.
Botanical composition and herbage yield will be measured again in the spring of 2008 to determine the impact of mowing on medusahead control.

Low-moisture blocks as attractants to promote grazing of medusahead

We trained livestock to find and consume a highly palatable low-moisture supplement offered in barrels marked with flags early in the spring at the Cook, Gonsalves, Bradford, Gallatin, Sonoma Land Trust and Dolcini ranches. Supplement was placed in areas of high medusahead density to attract livestock. A series of transects with grazing exclosures were established centered at the supplementation site and at a similar medusahead patch at least 300 m away from the supplement. We measured botanical composition, degree of grazing, and herbage height prior and after grazing in the spring of 2007. The molasses based supplement was very effective in attracting livestock to the area. Grazing use around supplement was very heavy, but highly concentrated, and decreased quickly with distance to supplement. Impacts on medusahead, productivity and botanical composition will be assessed at peak standing crop in the spring of 2008.

Medusahead phenology

Phenological information about medusahead and barbed goatgrass was collected in eleven counties during the growing seasons in 2006 and 2007. Data have been collated into a database where they will be joined with topographical and weather data to develop predictive models for phenological stage as a function of date, location and weather.

Preliminary analyses indicate that there are significant regional differences in the phenology of medusaehad. Whereas in Glenn and Stanislaus Counties medusahead reached late vegetative state in 20 April 2006, that phenological stage was reached until 8 May in Alameda and 4 May in Mendocino. These last two Counties are characterized by having greater rainfall and lower temperatures than the rest in the spring. We will fit predictive models using degree-days and other weather variables to forecast medusahead phenological stage for best timing of control treatments.

Germination and establishment of desirable grasses

We tested the hypothesis that medusahead has allelopathic effects on the seed germination and seedling growth of six desirable species. Germinations of desirable grasses were significantly delayed in association with medusahead seed germinating, awns, and litter such as inflorescence, inflorescence + straw, and straw, respectively. Oats and softchess seedling growth were significantly reduced in association with medusahead seed germinating, awns, and litter such as inflorescence, inflorescence + straw, and straw. Medusahead seeds and awns had allelopathic effects and delayed the seed germination of other annual species such as barley, oats, ryegrass, and softchess. Nasella pulchra germination was not affected by medusahead seeds or awns. Oats appeared to be the most sensitive species to the allelopathic effect of medusahead.

Dissemination and training

This project disseminated information about medusahead through training of high school, college, and graduate students, through field days, and by presenting information in workgroup meetings, and direct communication with land owners and managers.

One high school student (Evan Lee) from the Bay Area conducted a germination experiment to determine the relationship between degree of seed maturity and viability of medusahead and barbed goatgrass seeds. This information is crucial to determine the latest time when mowing can effectively control weed reproduction. Evan presented his results in a written report and in an oral presentation that was attended by approximately 60 people, mostly other high school students and their family members.

Our group shared results with the Rangeland Watershed Group of the Division of Agriculture and Natural Resources of the University of California at the Annual meeting during 11-13 December 2006. We made two presentations about medusahead control that were attended by approximately 44 people, mostly Extension Specialists, Farm Advisors, professors and graduate students. We prepared and distributed a draft informational brochure describing the use of precision grazing to control rangeland weeds. The brochure is included as an appendix to this report. It will be updated with the relevant information obtained by the present project.

Laca, PI of this project, attended Weed Day on 19 July 2007 and presented research results to a large audience composed of Cooperative Extension Specialists, Farm Advisors, graduate students, producers, professors, consultants, representatives of agrochemical companies, USDA-NRCS personnel, Caltrans personnel, etc. There were 94 people attending Weed Day.

Our group held its main annual meeting (Medusahead Day) at the Yeager ranch and at UC Davis on 20 July 2007. The meeting consisted of a field visit to see the results of precision grazing with sheep in the morning, and a series of presentations and discussions at the UCD campus in the afternoon. There were 24 participants representing seven institutions or enterprises. During this meeting we evaluated the work completed so far and assessed the need for changes. All participants discussed the performance of the group and voted unanimously that progress had been satisfactory or better. Therefore, no major changes in approach or activities were necessary.

Work to be completed

Due to the severe drought during the 2007 season, livestock water sources were dry and we were not able to conduct the grazing experiment with cattle at the Owens ranch. We plan to conduct this experiment this season, which so far has received good rainfall.

A second experiment with sheep is being conducted at the Yeager ranch during winter-spring 2008. We will evaluate the final results of the first grazing trial during 2008, and of the second grazing trial in 2009.

We will test a different spatial arrangement of low-moisture blocks in several ranches during the season of 2008. Given that supplement tubs seem to have a very localized impact, we will use more tubs with wider spacing.

This year we will complete the modeling of medusahead phenology and will incorporate the results into the websites for the Rangeland and Weed Research Information Centers. Because this year seems to have different rainfall amount and pattern than 2007, we will continue to collect phenology information as possible to create a database with general applicability.

Impacts and Contributions/Outcomes

This project benefits producers and consumers in several ways. First, we increased awareness about the invasive species problem. High school students and their families learned about this issue and are better prepared to make decisions that involve public areas such as regional parks that are infested with medusahead and other rangeland weeds. Several project participants and people who attended the field days learned to clearly distinguish medusahead from wild barley. Once they started looking for medusahead in their properties they realized that the problem is severe and that the value of their land and its productivity is negatively affected. Second, producers, agency personnel and consultants, as well as team members became familiar with the phenology and growth stages of medusahead. For example, they learned that medusahead seed disperses in late summer, so attempts to control it with fire in Fall are not very successful because seeds are already in the ground where fire temperatures are not sufficient to kill the seeds. Third, we applied grazing treatments in several ranches, with impact in several hundred acres. Approximately 20 acres were seeded with perennial and desirable annual species after precision grazing was applied. Finally, we have formed an effective group where we share information relevant to invasive species control and other rangeland management issues. We communicate by electronic mail and an internal wiki site that was created for the group. The linkages and communications established have been useful to disseminate the experience of individuals to the whole group.

The impact of this projects is significant in terms of the variety and number of people who have received information directly. We estimate that we have reached more than 300 individuals through field days, presentations, visits to ranches and scientific meetings. Many of these individuals are extension agents and participate in Regional Conservation districts and Weed Management Areas, as well as in federal and non-government agencies, and will certainly multiply the reach of our results. Our members have received invitations from other land management organizations to present our results. Overall, we have been very effective at communicating within our large group and with the broader clientele.


Jim Yeager
34791 Creeks Edge Road
Davis, CA 95616
Office Phone: 5307562423